1. Field of the Invention
The invention relates to a label-sensing device for a labeling machine, more particularly to a label-sensing device that can be adjusted to suit the actual ambient light condition.
2. Description of the Related Art
Commodities, such as beverage bottles, drug bottles, containers, and packaging boxes, are generally provided with a label to classify products, to indicate usage and other information, to display the trademark or logo of the manufacturer, etc. With the recent advancement in automation, automated attachment of labels to such commodities has taken the place of manual label attachment, and has become quite popular in the industry.
Referring to FIG. 1, a conventional label-sensing device for detecting movement of a label reel during a label-feeding operation of a labeling machine is shown to comprise a controller 1, a digital-to-analog (D/A) converter 2 coupled to the controller 1, a buffer 3 coupled to the D/A converter 2, an infrared sensor 4 coupled to the buffer 3, and a comparator circuit 5 coupled to the infrared sensor 4 and the controller 1. The controller 1 provides a binary-encoded signal to the D/A converter 2. According to the binary-encoded signal from the controller 1, the D/A converter 2 generates a corresponding analog voltage that is provided to the buffer 3. The infrared sensor 4 receives the analog voltage from the buffer 3, and generates a sensing light output having an intensity that corresponds to the analog voltage. The comparator circuit 5 receives a detected output from the infrared sensor 4, and compares the detected output with a predetermined reference voltage. The result of the comparison is provided to the controller 1 by the comparator circuit 5.
FIG. 2 is a schematic electrical circuit diagram of the conventional label-sensing device of FIG. 1. As shown, the D/A converter 2 has eight input pins (XD0-XD7) coupled to the controller 1. Thus, the controller 1 can provide 256 combinations of the binary-encoded signal to the D/A converter 2, thereby enabling the latter to generate 256 different analog voltages. A transmitter side of the infrared sensor 4 receives the analog voltage from the D/A converter 2 via the buffer 3. Thus, the intensity of the sensing light output at the transmitter side of the infrared sensor 4 depends on the magnitude of the analog voltage from the D/A converter 2. The sensing light output is directed to pass through one end of a label reel (not shown), which is being fed by a labeling machine (not shown), before being received by a receiver side of the infrared sensor 4. The label reel includes a backing paper strip and a plurality of labels releasably and successively adhered on the backing paper strip. The detected output at the receiver side of the infrared sensor 4 is weaker at portions of the label reel where the labels overlap with the backing paper strip, and is stronger at portions of the label reel where the labels do not overlap with the backing paper strip, e.g. at a clearance between each adjacent pair of the labels on the backing paper strip. The comparator circuit 5 compares the detected output from the receiver side of the infrared sensor 4 with a predetermined reference voltage that is set by resistors R22, R23 of a voltage-divider circuit, and generates a high or low logic output when the detected output is lower or higher than the reference voltage. The logic output of the comparator circuit 5 is received by the controller 1 and is recorded by the latter.
It is noted that the accuracy of the label-sensing device is affected by the actual ambient light condition. It is thus desirable to provide a label-sensing device that can be adjusted to ensure proper operation regardless of the actual ambient light condition.
Therefore, the main object of the present invention is to provide a label-sensing device for a labeling machine that can be adjusted to suit the actual ambient light condition.
According to this invention, a label-sensing device is adapted for use in a labeling machine to detect movement of a label reel during a label-feeding operation of the machine. The label reel includes a backing paper strip and a plurality of label reels releasably and successively adhered on the backing paper strip. The label-sensing device comprises a power supplying circuit, an infrared sensor, a voltage amplifier, and a controller. The power supplying circuit is adapted to supply a predetermined regulated DC voltage output. The infrared sensor includes an infrared transmitter coupled to the power supplying circuit, and an infrared receiver that forms a clearance with the infrared transmitter. The clearance is adapted to permit passage of one end of the label reel therethrough. The transmitter generates a sensing light output with an intensity that corresponds to the regulated DC voltage output. The sensing light output is directed by the transmitter so as to be adapted to pass through said one end of the label reel before being received by the receiver. The receiver has a detected output with a weaker first intensity upon detection of a first portion of the label reel where one of the labels overlaps with the backing paper strip, and with a stronger second intensity upon detection of a second portion of the label reel where the labels do not overlap with the backing paper strip. The voltage amplifier is coupled to the receiver for amplifying the detected output. The voltage amplifier generates a first signal when the detected output has the first intensity, and a second signal when the detected output has the second intensity. The controller, which is coupled to the voltage amplifier, converts the signal from the voltage amplifier into a corresponding detected value, and compares the detected value with an initial reference value to determine whether the first portion or the second portion of the label reel has passed through the clearance of the infrared sensor.
In the preferred embodiment, the controller automatically adjusts the initial reference value to be higher than the detected value corresponding to the first signal from the voltage amplifier upon detection by the controller that the initial reference value is lower than the detected value for the first signal, and to be lower than the detected value corresponding to the second signal from the voltage amplifier upon detection by the controller that the initial reference value is higher than the detected value for the second signal.